2.14 Electric fields
9 exam questions worth 19 marks. Write your answer, open the mark scheme, then give yourself the marks you earned. Your answers are saved on this device.
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In which direction do the electric field lines point around a negatively charged sphere?
Choose one answer.
Correct Not quite: the answer is Towards the sphere
Mark scheme
B: towards the sphere
Model answer
Towards the sphere (B), because field lines show the force on a positive charge, which is attracted.
Describe the electric field around a positively charged sphere.
Mark scheme
field lines point away from the sphere / radially outwards (1); the lines are closest together near the surface, so the field is strongest there (1)
Model answer
The field lines point radially away from the sphere. They are closest together near the surface, where the field is strongest.
State how the strength of the electric field around a charged sphere changes as the distance from the sphere increases. State how this shows on a field line diagram.
Mark scheme
the field strength decreases / gets weaker (1); the field lines get further apart (1)
Model answer
The field gets weaker as the distance increases, and the field lines get further apart.
Describe the electric field between two oppositely charged parallel plates.
Mark scheme
uniform / the same strength everywhere (field lines are straight, parallel and equally spaced) (1); direction from the positive plate to the negative plate (1)
Model answer
The field is uniform: the lines are straight, parallel and equally spaced, and point from the positive plate to the negative plate.
A charged object is placed in an electric field. State what the object experiences and explain why this is called a non-contact force.
Mark scheme
it experiences a force (1); because the force acts without the objects touching / the field exerts the force at a distance (1)
Model answer
It experiences a force. This is a non-contact force because it acts across the field without the objects touching.
Explain how a spark is produced when a charged object is brought close to an earthed conductor.
Mark scheme
there is a very strong electric field between the object and the conductor (1); the field ionises the air / pulls electrons from the air molecules, so the air can conduct (1); charge flows through the ionised air as a spark (1)
Model answer
A very strong electric field exists in the gap between the charged object and the conductor. The field ionises the air, so it becomes able to conduct. Charge then flows through the ionised air as a spark.
A negatively charged dust particle is between two horizontal plates. The top plate is positive and the bottom plate is negative. State the direction of the force on the particle and explain your answer.
Mark scheme
upwards / towards the positive plate (1); field lines go from positive to negative so are downwards (1); a negative charge is pushed in the opposite direction to the field lines (1)
Model answer
The force is upwards. The field lines point down from the positive plate to the negative plate, and a negative charge is pushed in the opposite direction to the field.
Explain why charge leaks away from a sharp point more easily than from a smooth surface.
Mark scheme
the field lines are closer together at a point (1); so the electric field is stronger there (1); the strong field can ionise the air / pull electrons from the air, allowing charge to flow away (1)
Model answer
At a sharp point the field lines are closer together, so the field is stronger. The strong field ionises the air, and the charge can then leak away.
Which of these correctly describes the field lines around a positively charged sphere?
Choose one answer.
Correct Not quite: the answer is They point away from the sphere
Mark scheme
B: They point away from the sphere
Model answer
They point away from the sphere (B).
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